1. Field of the Invention
The present invention relates to a hybrid sensor module, of which the overall height can be reduced, while a reduction in characteristic of the sensor module caused by the reduction in sensor size is prevented, and a sensing method using the same.
2. Description of the Related Art
In general, sensor modules serve to detect a signal component like a vector with a magnitude and direction on a two- or three-dimensional space. As for representative sensor modules, there are provided a geomagnetic sensor which detects the magnitude of the geomagnetic field existing on the three-dimensional space and an acceleration sensor which measures acceleration.
In particular, two-axis sensors are needed for detecting signal components existing on the two-dimensional space. When the two-axis sensors are operated in a state where they are placed in parallel to the surface of the earth, signal components output from two axes, that is, X and Y axes can be detected. Such signal components can be expressed by a sum of vectors with a magnitude and direction.
When the two-axis sensors are used, only the X- and Y-axis components of a vector can be measured. However, three-dimensional components should be all measured to detect a perfect signal. In order to measure a signal on the three-dimensional space, three sensors should be vertically arranged in such a manner that the respective sensor axes measure vector components of the signal. For this, three sensors having the same sensitivity should be arranged in parallel to the X, Y, and Z axes of an orthogonal coordinate system, respectively. In this structure, signal components existing on the three-dimensional space can be measured and then expressed as X-, Y-, and Z-axis components of the orthogonal coordinate system.
Currently, as for sensors used in mobile equipments, two-axis sensor modules are mainly adopted. This is because mobile equipments do not have such a sufficient space as to mount a three-axis sensor module. In the two-axis sensor module, two sensors are arranged vertically with each other on the X and Y planes. As for the two-axis sensor module, there are provided various types of sensors such as a fluxgate sensor, a magneto-resistance (MR) sensor, a magneto-impedance (MI) sensor and the like. In these sensors, however, three sensors cannot be implemented as one device. Therefore, a module is constructed in a hybrid-sensor type so as to implement a three-axis sensor module.
In the hybrid-sensor type module, the same kind of sensors are adopted on two axes, and a different kind of sensor is adopted on the other one axis. Then, it is possible to solve a problem occurring when a three-axis sensor module is implemented. For example, when a geomagnetic sensor is manufactured using the Micro Electro Mechanical Systems (MEMS) technique, X- and Y-axis sensors can be easily implemented on a silicon substrate. However, there are technical difficulties in implementing a Z-axis sensor. Further, although the Z-axis sensor is implemented, the characteristic thereof is considerably reduced, compared with those of the other two sensors. Furthermore, when three sensors are implemented as one device, the height of the device is increased. Therefore, it is difficult to adopt the device into mobile equipments.
As for a device for solving such a problem, a hybrid sensor module attracts attention. When three sensors with the same size are arranged to construct a three-axis sensor module, the Z-axis height of the sensor module makes it difficult to commonly use the sensor module. Therefore, as for the X- and Y-axis sensors, fluxgate-type sensors are adopted. As for the Z-axis sensor, an MR sensor or hall sensor is used so as to reduce the Z-axis height.
Meanwhile, a sensor expresses a signal component, existing on the three-dimensional space, as a sum of vectors with a magnitude and direction. Therefore, a direction where the sensor is disposed should coincide with a direction where the sensor actually senses the signal component.
FIG. 1 is a diagram showing X-, Y-, and Z-axis sensors constructed along a general orthogonal coordinate system. FIGS. 2A and 2B are diagrams showing conventional sensor modules, in which X-, Y-, and Z-axis sensors 22, 23, and 24 are arranged in parallel to the orthogonal coordinate system.
FIG. 2A shows a sensor module to which the sensors of FIG. 1 are applied. In the sensor module, the X-, Y-, and Z-axis sensors with a predetermined size l are arranged. FIG. 2B shows a hybrid sensor module in which the size of the Z-axis sensor is reduced in such a manner that the height of the Z-axis sensor decreases to a height l′.
As shown in FIGS. 2A and 2B, the conventional sensor module includes the X-, Y-, and Z-axis sensors 22, 23, and 24, which are attached on a printed circuit board (PCB) 21 so as to detect signal components existing on the three-dimensional space, and a signal processing circuit 25 which receives the detected signal components through a signal line connected to the respective sensors 22, 23, and 24 and then processes the signal components.
In FIGS. 2A and 2B, arrows indicate sensing directions of the respective sensors.
The sensor module having the X-, Y-, and Z-axis sensors arranged as shown in FIG. 2A has a relatively excellent sensor characteristic (for example, sensitivity), because the X-, Y-, and Z-axis sensors have a predetermined length l such that a certain sensor characteristic can be maintained. Because of the size of the sensors, or specifically, the size of the Z-axis sensor 24, the overall height of the sensor module increases. Therefore, it is difficult to apply the sensor module to mobile equipments which are gradually reduced in size.
To solve such a problem, the hybrid sensor module shown in FIG. 2B, in which the Z-axis sensor is smaller than the X- and Y-axis sensors 22 and 23, is frequently used. However, as the size of the sensor decreases, the characteristic thereof is considerably degraded. Therefore, the characteristic of the Z-axis sensor 24 of FIG. 2B is considerably degraded, compared with the other sensors. As a result, the overall characteristic of the sensor module is degraded.